Polynucleotide: Definition, Types, & Examples

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Polynucleotide Definition

The polynucleotide is a polymer of nucleotides. It comprises a long, linear series of nucleotides that are linked together with ester linkages. The bond formed to join the hydroxyl group of sugar component of a nucleotide with phosphoryl group of another nucleotide.

What is Polynucleotide?

Nucleic acid polymers are also made up of nucleotides, thus they act as a building block or monomer of nucleic acids. The structure of nucleotide is comprised of three subunits, a nucleobase, a five-carbon sugar, and a phosphate group.

It is an organic molecule that is made up of mainly two types of sugars, which are ribose sugar and deoxyribose sugar. RNA has the sugar component of ribose whereas DNA comprises deoxyribose sugar.

Two adjacent nucleotide monomers are connected by a phosphate group and form the backbone of a nucleic acid. The DNA has the opposite orientation of two strands, which allows complementary base pairing between nitrogenous bases.

Another form of nucleotide is cyclic. When the phosphate group is linked twice to the hydroxyl group of the constituent sugar, it forms cyclic nucleotides. Nucleotides are classified into two types that are purines and pyrimidines.

Adenine and guanine bases are included in purines whereas thymine and cytosine are pyrimidines. In RNA, thymine is replaced with uracil. The structure of uracil differs from thymine by the presence of methyl in thymine.

However, both purines and pyrimidine are aromatic compounds but they can be distinguished by their chemical structure. Nucleotides are classified as mononucleotides, dinucleotides, oligonucleotides, and polynucleotides.

Polynucleotide Characteristics

Several nucleotides form a polynucleotide whereas an oligonucleotide is made up of only a few nucleotides. A nitrogenous base, a pentose moiety, and a phosphate group are the components of a nucleotide.

The phosphoryl group of a nucleotide connects with the hydroxyl group of the sugar component of another nucleotide to join two nucleotides by ester linkage. Besides polynucleotides, other major biopolymers include polysaccharides and polypeptides.

Polynucleotide Examples

Examples are DNA and RNA. DNA or deoxyribonucleic acid is a polynucleotide that comprises several nucleotides. This monomeric unit is joined by 3’, 5’ phosphodiester linkages that include esterification of the 5’-phosphoric group with a 3’-hydroxyl group of the adjacent nucleotide. Each nucleotide is made up of three components named phosphoric acid, deoxyribose sugar, and a nitrogenous base.

There are four nitrogenous bases such as adenine, thymine, guanine, and cytosine. DNA is a double-helical structure that comprises complementarily paired nucleobases and antiparallel strands. Adenine always pairs with thymine similarly cytosine pairs with guanine. The hydrogen bond joins the two nucleobases.

Another polynucleotide is RNA or ribonucleic acid, which comprises a long chain of nucleotides. A ribose sugar, phosphate group, and nucleobases are the components of each monomeric unit of RNA. The adjacent ribose sugars are joined by the phosphate group that connects 3’ of the ribose to 5’ of another ribose.

In the 1’ of a ribose sugar, the nitrogenous base connects which are of four types including adenine, cytosine, guanine, and uracil. The backbone of the RNA is made up of ribose sugar and the phosphate group. RNA is mainly of three types including messenger RNA, transfer RNA, and ribosomal RNA.

Biological Importance of Polynucleotide

Major natural polynucleotides are DNA and RNA. DNA is the genetic material in most living organisms that also code for amino acid sequence during translation. All the genetic information and instructions are carried out by DNA.

These instructions are essential for various cellular activities such as transcription, translation, etc. some viruses include RNA as genetic material but in most organisms, RNA is involved in translation, post-transcriptional modifications, gene regulation, and DNA replication.

mRNA, tRNA, and rRNA are mainly involved in protein synthesis whereas snRNA, and snoRNA helps in DNA replication and post-transcriptional modifications. Other uses of polynucleotides are also in research and experiments. They are used in a polymerase chain reaction or DNA sequencing.

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